Near-perfect absorption throughout the visible using ultra-thin metal films on index-near-zero substrates [Invited]

Krayer, Lisa J.; Kim, Jong Bum; Munday, Jeremy N.

doi:10.1364/ome.9.000330

Cited by 23 publications

(21 citation statements)

References 37 publications

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“…25,26 When the laser pulse hits the sample, most of the energy is absorbed by the Pt layer. While Pt has a strong optical absorption (~10 7 cm -1 ) 28 , enhanced by the Etalon effect 29 , the absorption in GGG|YIG (10 cm -1 ) is essentially negligible. 30,31 The electrons in Pt are heated within a few tens of femtoseconds 18 .…”

Section: Takedownmentioning

confidence: 99%

Temperature dependence of the picosecond spin Seebeck effect

Kholid

Hamara

Terschanski

et al. 2021

Applied Physics Letters

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We performed temperature-dependent optical pump -THz emission measurements in Y3Fe5O12 (YIG)|Pt from 5 K to room temperature in the presence of an externally applied magnetic field. We study the temperature dependence of the spin Seebeck effect and observe a continuous increase as temperature is decreased, opposite to what is observed in electrical measurements where the spin Seebeck effect is suppressed as 0 K is approached. By quantitatively analysing the different contributions we isolate the temperature dependence of the spin-mixing conductance and observe features that are correlated to the bands of magnon spectrum in YIG.The longitudinal spin Seebeck effect (LSSE) 1 describes the transfer of a spin current from a magnetic insulator driven by a temperature gradient. An adjacent heavy metal (HM) layer with large spin orbit coupling is typically used to convert the spin current into an electrical signal via the inverse spin Hall effect (ISHE). 2,3 The LSSE has been measured in a variety of different materials such as ferromagnets 1,4,5 , anti-ferromagnets 6,7 and paramagnets. 8 Magnetic insulators (MI) such as Y3Fe5O12 (Yttrium Iron Garnet -YIG) are particularly interesting for studies on the LSSE since the absence of electron charge transport allows the roles of magnons and phonons to be identified in the spin transfer. 1,3,9,10 Temperature, thickness and magnetic field dependence studies have contributed to a phenomenological picture of magnon-driven spin current. [11][12][13][14][15] A temperature gradient across the magnetic insulator thickness leads to the diffusion of thermal magnons that accumulate at the interface with the HM. 16,17 The temperature dependence of the magnon propagation length m results in a characteristic peak in the SSE signal at low temperature when the thickness of the MI is comparable to m . 12 Low frequency magnons play a dominant role due to their large population and

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Section: Takedownmentioning

confidence: 99%

Temperature dependence of the picosecond spin Seebeck effect

Kholid

Hamara

Terschanski

et al. 2021

Applied Physics Letters

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“…Such homogeneous ultrathin films are attractive for applications in coloring, filtering, absorption enhancement in photovoltaic applications, infrared absorbers and emitters, and in reconfigurable flat optics. [11][12][13][14][15][16][17][18][19][20] Epsilon-near-zero (ENZ) materials are one such class of thin film materials that have gained much interest in recent times. [21,22] The real part of permittivity (ε 0 ) of ENZ materials becomes zero at the zero-epsilon wavelength (λ ZE ), such that ε 0 is positive (negative) at shorter (longer) wavelengths.…”

Section: Introductionmentioning

confidence: 99%

Tailoring Infrared Absorption and Thermal Emission with Ultrathin Film Interferences in Epsilon‐Near‐Zero Media

Johns

Chattopadhyay

Mitra

2021

Advanced Photonics Research

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Engineering modal dispersions of ultrathin, planar structures enables significant control over infrared perfect absorption (PA) and thermal emission characteristics. Herein, the optical response of ultrathin, low loss, epsilon‐near‐zero (ENZ) films on reflecting surfaces is simulated to investigate the wavelength and angular ranges over which they absorb and emit radiation most efficiently and identify the design parameters that tailor the ENZ mode dispersion of the system. A generic interference model is shown to elucidate the underlying physics of these ultrathin film absorption resonances, occurring well below the conventional quarter‐wavelength thickness limit. While the absorption is spectrally limited to wavelengths where the ENZ film is optically a dielectric with refractive index below unity, the angular spread is delimited by the material dispersion. Further, these resonant interferences are understood to arise from universal wave phenomena, realizable in simple planar structures having appropriate refractive index contrast, not restricted to ENZ materials. The results show that appropriate choice of material, film thickness and loss allows tailoring the modal dispersions, which enables precise directional control and wide tunability in spectral range (width ≈0.1–1.0 μm) of PA and thermal emission, paving the way towards efficient ENZ‐based infrared optical and thermal coatings.

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“…However, in the nanoscale, poor adhesion of silver to commonly used substrates such as ultra-smooth fused silica or sapphire results in a rough metal-free surface, which increases the scattering losses of the metal film. To tackle this problem, a number of approaches have been proposed, the most prominent being the use of wetting materials exhibiting good adhesion to both silver and the substrate [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. The greatest reduction of surface roughness-up to an order of magnitude-is observed when the substrate is wetted with a~2-nm-thick layer of germanium prior to the deposition of silver [2,11].…”

Section: Introductionmentioning

confidence: 99%

“…Instead of covering the silver layer with a material which exhibits grain boundary diffusion within silver, we introduce another layer below germanium, which is made of gold. Germanium has been proven to segregate within the nanolayers of both silver and gold [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], as Ag and Au exhibit many crucial similarities, like their atomic radius and lattice constant. However, the free enthalpy of the segregation process is influenced by many quantities in which silver and gold differ-e.g., bulk modulus, shear modulus and surface energies [28,42].…”

Section: Introductionmentioning

confidence: 99%

Inhibiting the Segregation of Germanium in Silver Nanolayers

2020

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It is generally acknowledged that using germanium as a wetting film for silver nanolayers decreases the surface roughness of the metal. However, germanium atoms also tend to segregate towards the surface of silver films, increasing ohmic losses in the structure. Here we propose an Au/Ge/Ag based structure where the segregation of germanium in silver is inhibited. X-ray photoelectron spectroscopy (XPS) results show that for the Au/Ge/Ag system, the surface concentration of germanium drops by an order of magnitude relative to multilayers containing only one type of metal (Ag or Au). We have also observed that the time-dependent decrease in the reflectivity due to localized surface plasmon excitation is less prominent in the case of the Au/Ge/Ag structure than in the case of Ag/Ge/Ag. We provide XPS as well as optical reflectometry results to support that claim.

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Near-perfect absorption throughout the visible using ultra-thin metal films on index-near-zero substrates [Invited]

Cited by 23 publications

References 37 publications

Temperature dependence of the picosecond spin Seebeck effect

Temperature dependence of the picosecond spin Seebeck effect

Tailoring Infrared Absorption and Thermal Emission with Ultrathin Film Interferences in Epsilon‐Near‐Zero Media

Inhibiting the Segregation of Germanium in Silver Nanolayers

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